Eradicated unintentional incorporated donor-type impurities of ZnO

Impurity control is essential for semiconductor doping. Through the systematic analysis of pollution sources, we determined that the residual electrons of as-grown unintentional doped zinc oxide (ZnO) films were derived from the unintentional incorporation of silicon, which grown by molecular beam epitaxy. At the same time, it was determined that unforeseen donor-type impurities (boron, carbon, chlorine and fluorine) were introduced during the nitrogen doping process. By subjecting the sources of the contamination to a surface passivation process, these donor-type impurities are controlled at a tolerable level. The residual electrons concentration of the unintentional doped ZnO film was lowered to 1 × 1015 cm-3, and the mobility was 155 cm2/V·s. Nitrogen-doped ZnO films exhibited p-type conductivity, with a hole concentration of 2 × 1016 cm-3 and a mobility of 10 cm2/V·s. Our results provide a pure foundation for further research on p-type doping of ZnO.